In the Chinese patent application CN1861443A titled “Method of Motor Control”, it disclosed a method for controlling motor in background, which adopts the velocity ring control to fulfill the PI control for the rotary speed of motor rotor, then control the torque of motor through the quadrature current and d-axis current adjustment for motor. This invention provides a motor control method for electric vehicle, which predetermined the quadrature target current according to the angular velocity of motor and predetermined the d-axis target current according to the torque of motor; detect and collect the 3-phase current of motor, meanwhile, the rotary transformer may detect the rotor position of motor and the revolving decoding unit may measure the angle of rotor; convert the 3-phase current of motor into the actual d-axis current and quadrature current according to the Park conversion and Clark conversion of rotor position angle; take the difference between the target current and actual current as the input of current ring for PI adjustment to output the required d-axis current and required quadrature current; output the required d-axis current and required quadrature current according to PI adjustment and calculate the 3-phase voltage value according to the motor rotor angle; and obtain the pulse width modulation control waveform from the 3-phase voltage, convert the DC into relevant AC to drive the motor.
The above mentioned velocity ring feedback control or current ring feedback control are only the basis of motor control. During practices, for complex and varying road surface cases and modes, thus, the decision making must be combined with various parameters of vehicle, and the current service conditions of electric vehicle, with the special control mode, calculate the target d-axis current and quadrature current, and finally given through PI adjustment to prevent the motor out-of-control.
One of the modes of electric vehicle is the skid mode. For example, when the vehicle travels from a normal surface of road into a smooth surface, such as an icy surface with very low friction, the situation equals to the load of motor suddenly reduced, due to sudden unload, the rotor of motor accelerates, the generated surge current and voltage may cause the protection of intelligent power module (IPM), directly cause the motor out-of-control, which is unallowable during the normal travel. On the contrary, when the vehicle is on the smooth surface of road, the motor may only output very low torque to ensure the normal travel of vehicle, but when the vehicle travels from the smooth surface to a section with normal friction of road surface, i.e., the situation equals to suddenly apply a load on the motor, the sudden growth of load may cause the torque of motor suddenly reduced at very low output, and even stall. This case may cause the protection of motor controller, moreover, during extreme case, i.e. blocked rotor, all the electric power may be converted into the heat of motor winding, which may cause the winding overheated. Both cases mentioned above are generally called “skid mode”. Under these cases, due to sudden increasing or decreasing of motor rotary speed, the out-of-control of motor may be caused.
There is no method or apparatus in the existing motor control strategys for controlling motor for electric vehicle aimed at the skid mode.